Photographic film unit

ABSTRACT

A self-developing photographic film unit adapted to be processed by a viscous liquid processing composition distributed within the film unit from the leading end toward the trailing end by movement of the film unit between a pair of pressure-applying members. The film unit includes a photosensitive sheet having a trailing end section, a transparent second sheet having a trailing end section, located in face-to-face relation with the photosensitive sheet and a retaining sheet engaged around and secured to the trailing end sections of the photosensitive and second sheets. The film unit is designed to remain intact following image formation in the region between sheets and a spacing element, which may be generally comb-shaped, is secured between the retaining sheet and the surfaces of the trailing end sections of the sheets to provide liquid trapping spaces located externally of the image-containing region between the sheets for collecting and retaining excess processing liquid overrun.

[ June 11, 1974 PHOTOGRAPHIC FILM UNIT [75] Inventor:

[73] Assignee: Polaroid Corporation, Cambridge,

Mass.

[22] Filed: Apr. 2, 1971 [21] Appl. No.: 130,609

Related US. Application Data [63] Continuation-in-part of Ser. No. 726,252, May 2, 1968, abandoned, which is a continuation-in-part of Ser. No. 721,231, April 15, 1968, abandoned.

[52 us. Cl. 96/76 (3, 96/29 R 51 im. Cl G03c l/48 581 Field of Search 96/76, 29; 95/13 [56] References Cited UNITED STATES PATENTS 2,627,459 2/1953 Land 96/29 2,627,460 2/1953 Land 96/29' 2,686,716 8/1954 Land 96/76 2,686,717 8/1954 Land t 96/29 2,906,181 9/1959 Booth 95/13 3,053,160 9/1962 Bachelder r 96/76 3,352,674 11/1967 Harvey 96/76 3,415,646 12/1968 Land 96/76 Richard J. Chen, Winchester, Mass.

Primary Examiner-Norman G. Torchin Assistant Examiner.lohn L. Goodrow 57 ABSTRACT A self-developing photographic film unit adapted to be processed by a viscous liquid processing composition distributed within the film unit from the leading end toward the trailing end by movement of the film unit between a pair of pressure-applying members. The film unit includes a photosensitive sheet having a trailing end section, a transparent second sheet having a trailing end Section, located in face-to-face relation with the photosensitive sheet and a retaining sheet engaged around and secured to the trailing end sections of the photosensitive and second sheets. The film unit is designed to remain intact following image formation in the region between Sheets and a Spacing element, which may be generally comb-shaped, is secured between the retaining sheet and the surfaces of the trailing end sections of the sheets to provide liquid trapping spaces located externally of the image-containing region between the sheets for collecting and retaining excess processing liquid overrun.

15 Claims, 9 Drawing Figures amsllza PA """imln m4 SHEET 10F 3 PATENTEBJuun an 3.81 SL128 sum 2 or a 290M (5. 6n!- ATTORNEYS PATENTEDJUNH m4 3816328 SHEET 3 OF 3 INVENTOR.

25W amd M 290M 4'. 150% 4 ATTORNEYS PHOTOGRAPHIC FILM UNIT This application is a continuation-in-part of my copending application Ser. No. 726,252 filed May 2, 1968, as a continuation-in-part of my application Ser. No. 721,231 filed Apr. 15, 1968, entitled Photographic Film Unit, both of which applications are now abandoned.

The present invention is illustrated as incorporated in a film unit of the type shown and described in the copending US. Patent application of Edwin H. Land et al. Ser. No. 622,286, filed Mar. 10, 1967 and now abandoned, adapted to be processed to produce a photographic print, preferably in full color, by a diffusion transfer process. As previously noted, film units of this type generally include a photosensitive sheet, a transparent second or image-receiving sheet through which the photosensitive sheet is exposed and an image formed between the sheets is viewed, binding means secured around the margins of the sheets to retain them in face-to-face relation during exposure and subsequent processing and viewing, and a rupturable container of a viscous processing liquid attached to the sheets, the liquid adapted, when distributed between the sheets in contact with the exposed photosensitive material, to produce a diffusion transfer image, preferably in full color, visible through the transparent second sheet. Processing of the film unit is accomplished by passing it between a pair of juxtaposed pressureapplying members, beginning with the container, to rupture the container and spread its liquid contents in a layer within the film unit toward the opposite end thereof (termed the trailing end) to effectuate positive image formation by a diffusion transfer process. The processing liquid adheres together the layers of the film unit between which it is spread to form a laminate and contains an opacifying agent providing a background for the transfer image formed between the layer of processing liquid and the transparent second sheet. The laminate thus formed contains a protectively enclosed image and is retained intact thereafter as a photographic print.

The processing liquid distributed in a layer within the film unit includes a viscous aqueous alkaline solution adapted to initiate a diffusion transfer process involving the formation of an image-wise distribution of imageproviding substances in an exposed photosensitive layer and transfer of the image-providing substances by diffusion to a juxtaposed image-receiving layer where they form a visible image. In order to insure that a predetermined exposed area to be processed is completely covered by a layer of predetermined uniform thickness of the aqueous alkaline processing composition, it is the usual practice to supply, in the container, a quantity of liquid in excess of the minimum amount required. For this reason and because of the highly viscous and caustic nature of the liquid processing composition presents a danger to both the user of the film unit and the apparatus in which it is employed, it is important that means be provided for collecting and retaining excess processing liquid within the film unit so as to prevent escape of the liquid from the film unit during and subsequent to spreading therewithin. Heretofore, it has been the practice to prevent overrun and escape of the processing liquid beyond the trailing ends of the sheets (as well as at their lateral margins) by extending. the trailing end portions of the sheets and providing spacing elements between the extended end portions of the sheets adapted to space apart the pressure-applying members employed to spread the processing liquid during movement of the extended trailing end portions of the sheets between the pressure-applying members and thereby provide a liquid reservoir between the extended trailing end portions in which excess liquid is collected and retained. The extent that the trailing end portions are extended is dependent upon both the amount and distribution of the excess liquid and must be of sufficient length to retain all excess liquid spread beyond the distal edges of the areas of these sheets to be processed.

The film unit of the invention differs from the usual prior art film unit in two important respects which materially alter and increase the seriousness of the problems of collecting and retaining excess processing liquid. In the present film unit, the layer containing the diffusion transfer image is not separated from the processed photosensitive layer and/or the layer of processing liquid, but the film unit is maintained intact as a laminate following processing with the imagecontaining layer sandwiched between two outer support layers or sheets; and the sheets of the film unit are bound to one another at their margins by a sheet material which forrns the margins of the finished photographic print and, accordingly, is relatively narrow as compared to the size of the image area. The latter means that, of necessity, the space within the film unit at the trailing end thereof available for collecting and retaining excess processing liquid not only is extremely limited but is very close to, if not in direct communication with, the region of the laminate between the outer support sheets containing the visible positive image; and enhances the problem of providing sufficient space or volume within the film unit in which to collect and retain the excess processing liquid, while creating the additional problem of preventing flowback of the excess processing liquid into the image area and the problem presented by a reservoir of excess processing liquid located immediately adjacent the image area where it is available to migrate back into the image area to discolor or otherwise impair the visible image.

Objects of the invention are: to provide in a film unit of the type described, novel and improved means for collecting and retaining excess processing liquid in a relatively small space while assuring that the liquid is prevented from escaping from the film unit and that excess liquid does not flow back or migrate back into the image area of the film unit; and to provide means for collecting and retaining excess processing liquid externally of the sheets between which the image is contained.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the product possessing the features, properties and the relation of components which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view, partially in section,

showing a film unit embodying the invention;

FIG. 3 is an enlarged perspective view of a portion of one of the aforesaid components, namely a spacing element;

FIG. 4 is a view similar to FIG. 3 illustrating another embodiment of a spacing element similar to that shown in FIG. 3.

FIG. 5 is a longitudinal, sectional view showing the film unit of FIG. 1 and illustrating the method of processing the film unit;

FIGS. 6 and 7 are enlarged, sectional views similar to FIG. 5, showing the portion of the film unit in which excess processing liquid is collected and retained and illustrating the way in which the film unit performs this function; and

FIG. 8 is a perspective view, similar to FIG. 3, of another embodiment of a spacing element; and

FIG. 9 is a sectional view, similar to FIG. 5, illustrating a film unit incorporating the spacing element of FIG. 8.

The film unit of the invention adapted to the performance of a number of different image-forming processes and particularly to the production of a positive photographic print preferably in full color produced by a diffusion-transfer process in which a photographic image-recording medium including a photosensitive material such as silver halide is exposed to form an image (latent) therein and is treated by wetting with a liquid processing agent to develop the image in the image-recording medium, form an imagewise distribution of transferable image-providing substances and transfer the image-providing substances by diffusion to an image-receptive stratum in which they are immobilized to form a visible positive image. The film unit may comprise materials for producing a black-and-white print according to a process such as disclosed in the US. Patents of Edwin H. Land, No. 2,543,181, granted Feb. 27, 1951, and No. 2,662,822, granted Dec. 15, 1953. In this embodiment, the film unit may comprise an image-recording medium including, as the photosensitive material, a silver halide emulsion; a liquid processing agent including a silver halide developer and a silver complexing agent; and the material required to provide a silver precipitating environment in an imagereceptive stratum of the film unit during processing. The processing liquid is distributed in contact with the layer containing the exposed image-recording medium for permeation therein to develop the latent image and form a soluble silver complex from unexposed silver halide which is transferred by diffusion to animagereceiving stratum where it is reduced to silver in the presence of a silver precipitant to form a visible posi-' tive image. The silver precipitating environment may be provided initially as a layer or stratum on one of a pair of superposed elements comprising the film unit, preferably an element different from the one including the image-recording medium, and/or in the liquid composition distributed in a layer between th elements.

A preferred embodiment of the film unit of the invention includes all of the materials and reagents required to produce a full color photographic print by a process such as disclosed in US. Pat. No. 2,983,606, issued May 9, 1961, in the name of Howard G. Rogers. This patent discloses a photosensitive element including a silver halide emulsion and a dye developer, that is, a dye which is a silver halide developing agent; a second or image-receiving element including an imagereceiving layer of a dyeable material; and a processing 4 liquid in which the dye developer is soluble. The photosensitive and image-receiving elements are superposed with the emulsion and image-receiving layers in faceto-face relation and the processing liquid is distributed in a uniform layer between and in contact therewith for permeation into the photosensitive layer where it initiates development of exposed silver halide. The dye developer is immobilized or precipitated in exposed areas as a consequence of development while in unexposed areas and partially exposed areas of the emulsion, the dye developer remains unreacted and diffusible thereby providing an imagewise distribution of unoxidized dye developer which is transferred, at least in part, by diffusion to the image-receiving layer without altering the imagewise distribution of the dye developer, to form a reversed or positive color image of the developed latent image in the emulsion. Multicolor transfer images are obtained utilizing dye developers, for example, by employing an integral multilayer photosensitive element such as illustrated in FIG. 9 of the 2,983,606 Patent, including at least two selectively sensitized overlying photosensitive strata on a single support. A typical photosensitive element of this type comprises a support carrying a red sensitive silver halide emulsion stratum, a green sensitive silver halide emulsion stratum and a blue sensitive silver halide emulsion stratum, the emulsions having associated therewith, respectively, for example, a cyan developer, a magenta dye developer and a yellow dye developer. Each set of silver halide emulsion and associated dye developer strata may be separated from other sets by suitable in-' terlayers formed, for example, of gelatin or polyvinyl alcohol. In the example given, the dye developers are preferably selected for their ability to provide colors useful in producing a full color image by a subtractive process and may be incorporated in the respective silver halide emulsion with which they are associated or in a separate layer behind their respective silver halide emulsion. In certain instances, a yellow filter is incorporated located in front of the green sensitive emulsion and comprising a yellow dye developer or a separate layer of a yellow filter material.

Reference is now made to FIGS. 1, 2, and 5 of the drawings wherein there is illustrated a photographic film unit 10 embodying the invention, the thickness of the materials being exaggerated for purposes of clarity of illustrationFilm unit 10 comprises a photosensitive or image-recording sheet 12, a second or imagereceiving sheet 14 and a rupturable container 16 holding a quantity of processing liquid 18. Sheets 12 and 14 are preferably, although not necessarily, rectangular and coextensive with one another and are arranged in superposed face-to-fac'e contact with at least the lateral edges of each sheet aligned with the lateral edges of the other. The two sheets are retained in superposed relation by a binding element 20 in the form of a rectangular sheet larger than either of the photosensitive or image-receiving sheets and secured to the two sheets at the margins thereof. Binding element 20 is in the general form of a frame having a large rectangular opening 22 defining the extent of the image produced in the film unit, surrounded by lateral edge portions 24 and end portions 26 and 28. Sheet 12 includes lateral marginal portions 30 and an end marginal portion 34 and sheet 14 includes lateral marginal portions 32 and an end marginal portion 36 with the lateral and end marginal portions of the two sheets being located in face-to-face contact, preferably with the edges of the lateral mar ginal portions in alignment. The lateral edge portions 24 and end portion 28 of binding element are secured around and to, respectively, lateral marginal portions 30 and 32 of sheets 12 and 14 and end marginal portions 34 and 36 of the sheetseffectively binding the two sheets to one another along three sides thereof. In a preferred form of film unit adapted to produce a reflection print surrounded by a white border and viewed against a white background, at least binding element 20 is formed of an opaque, white material and container 16 may also include a white outer coating to provide a more aesthetically pleasing product.

Container 16 is of the type shown in US. Pat. No. 2,543,181, formed by folding a rectangular blank of a fluid impervious sheet material medially and sealing the marginal sections of the blank to one another to form a cavity for containing processing liquid 18. The seal between longitudinal marginal sections 38 of the container is weaker than the end seals so that upon the application of a predetermined compressive force to the walls of the container in the region of the liquid-filled cavity, there will be generated within the liquid hydraulic pressure sufficient to separate longitudinal marginal sections 38 throughout the major portion of their length to form a discharge mouth at least equal in length to the length of the cavity and the width of opening 22 through which processing liquid 18 is discharged. Container 16 is attached to the sheets at the edges thereof opposite end portions 34 and 36, preferably with the longitudinal edge of the container butted against the edges of the sheets and with the discharge passage of the container aligned with the facing surfaces of the sheets. Sheets 12 and 14 include, respectively, end marginal portions 40 and 42 and the means for coupling the container to the sheets include end portion 26 of binding element 20 secured to end marginal portion 42 of sheet 14 and longitudinal marginal sections 38 of the container so as to bridge the container and sheet 14; and a strip 44 secured to end marginal portion 40 of sheet 12 and the other longitudinal marginal section 38 of the container to bridge the gap between the container and sheet 12. The binding element and strip 44 cooperate to provide a liquidtight seal between the marginal sections of the container defining the discharge mouth thereof and sheets 12 and 14; and form a conduit for conducting the liquid from the container between the sheets at end marginal portions 40 and 42 thereof.

The most useful and advantageous film unit insofar as packaging, storing, handling, exposure and process-v ing are concerned, is one characterized by an integral, unitary, laminate form of structure designed so that its integrity may be maintained during and after exposure and processing; and a structure that is sturdy, has some flexibility and can be handled and manipulated by mechanical means without damage to produce a useful and attractive photographic print. A useful and attractive photographic print can be described as being substantially flat or planar and without a tendency to curl as the result of temperature and humidity changes; as being relatively rigid and inflexible as opposed to being limp or easily bent; as having a uniform white border surrounding a well-defined rectangular image that extends to the border; and a protective coating or covering for the image permitting the print to be handled and stored without the necessity for taking special precautions to avoid damage and deterioration. THe structure and composition of components of the film unit of the invention combine to provide a film unit meeting these criteria and specially adapted, when processed, to provide a useful and attractive photographic print, preferably in full color, having the foregoing characteristics.

In order to provide a rigid durable structure having an integrity which is maintained from the time of assembly (during manufacture) to the finished print and providing a protective environment for the photosensitive medium as well as the final image, while permitting exposure of the photosensitive medium and viewing of the final image, at least one of the sheets of the film unit is formed of a transparent material. In the embodiment shown the second or image-receiving sheet is transparent and the photosensitive medium is exposed and the final image is viewed through the image-receiving sheet which functions to protect both the image-recording medium and the final image. In other embodiments of the film unit the photo-sensitive sheet may be transparent depending upon the manner in which the imagerecording medium is exposed and the final image is formed and viewed. The transparent image-receiving sheet may be formed of a conventional film base material such as cellulose triacetate coated on its inner surface with one or more layers providing an appropriate environment for the formation of a diffusion transfer image. In a film unit designed to produce a color image in terms of a dye developer, the image-receiving sheet may be prepared as disclosed in the following example, by coating a transparent cellulose triacetate film base in succession with the following layers:

1. the partial butyl ester of polyethylene/maleic anhydride copolymer prepared by refluxing, for 14 hours, v 300 grams of high viscosity poly- (ethylene/maleic anhydride), 140 grams of n-butyl alcohol and lcc. of percent phosphoric acid to provide a polymeric acid layer approximately 0.75 mils. thick;

2. a solution of hydroxypropyl cellulose in water to provide a polymeric spacer layer approximately 0.075 mils, thick; and

3. a 2:1 mixture,by weight, of polyvinyl alcohol and poly-4-vinylpyridine, at a coverage of approximately 600 mgs./ft. to provide a polymeric imagereceiving layer approximately 0.40 mils. thick.

In a preferred embodiment of the film unit useful in color photography and incorporating an imagereceiving sheet prepared as described above, the image-recording sheet is preferably opaque to actinic light and is prepared, for example, by coating in succession on a gelatin subbed opaque cellulose triacetate film base, the-following layers:

1. a layer of cyan dye developer l,4-bis-(B- [hydroquinonyl-a-methyl]-ethylamino) 5,8- dihydroxy-anthraquinone dispersed in gelatin and coated at a coverage of about 150 mgs./ft. of dye and about 200 mgs./ft. of gelatin; and

2. a red-sensitive gelatino-silver iodobromide emulsion coated at a coverage of about 200 mgs./ft. of silver and about mgs./ft. of gelatin;

3. a layer of gelatin coated at a coverage of about 200 mgs/ft 4. a layer of the magenta dye developer Z-(p-[B- hydroquinonylethyl]-phenylazo)-4-isopropoxy-l naphthol dispersed in gelatin and coated at a cover- 7 age of 70 mgs./ft. of dye and about 100 lngsjft. of gelatin;

5. a green-sensitive gelatino-silver iodobromide emulsion coated at a coverage of about 100 mgs./ft? of silver and 60 mgs./ft. of gelatin;

6. a layer of gelatin coated at a coverage of about 150 mgs./ft.

7. a layer of the yellow dye developer 4-(p-[B hyd roquinonylethyl -phenylazo )-3-( N-nhexylcarboxamido)- l -phenyl-5-pyrazolone dispersed in gelatin and coated at a coverage of about 40 mgs./ft. of dye and 50 mgs./ft. of gelatin;

8. a blue-sensitive gelatino-silver iodobromide emulsion coated at a coverage of about 60 mgs./ft. of Silver and %t Q1s-!fto llfli,....

a layer containing 4"-methylphenyl hydroquinone dispersed in gelatin and coated at a coverage of about mgs./ft. of 4-methyl,phenyl hydroquinone and about 30 mgs./ft. of gelatin.

The image-recording and image-receiving elements may incorporate other strata and coatings commonly employed in photographic products of this type such as optical coatings for preventing halation and reflection and otherwise improve the optical properties of the sheet material and to facilitate and improve exposure and viewing of the final image.

The embodiment of the film unit illustrated and described hercin is adapted to be exposed and processed to produce a multicolor dye transfer image in a dyeable polymeric layer located between a transparent film on which the dyeable polymeric layer is supported and an opaque layer located between the image and the photosensitive medium. This opaque layer comprises the liquid contents 18 of container 16 provided in sufficient quantity to form a layer of predetermined thickness, e.g., of the order of .004 inch, when distributed uniformly between the sheets over an area at least coextensive with opening 22 in binding element 20. In order to insure that the quantity of liquid 18 supplied in the container is at least sufficient to form a layer of the desired minimum thickness and extent, the processing liquid is provided in a quantity in excess of the minimum amount required. The processing liquid contained in container 16 comprises an aqueous alkaline solution having a pH at which the dye developers are soluble and diffusible and contains an opacifying agent in a quantity sufficient to mask the dye developers retained in the image-recording layer (laminate) subsequent to processing; and a film-forming viscosity increasing agent or agents to facilitate rupture of the container and distribution of the liquid processing composition and help in maintaining the layer of processing compo sition as a structurally stable layer tending to bind the sheets to one another.

As a general rule, the opacifying agent will be present in the layer of liquid spread between the transparent image-receiving sheet and the opaque image-recording sheet in a concentration sufficient to prevent further exposure of the image-recording medium by actinic radiation transmitted by the transparent image-receiving sheet. Because the silver halide emulsion or emulsions comprising the image-recording strata are thus protected against exposure by incident actinic radiation at one major surface by the opaque processing composition and at the remaining major surface by the opaque support sheet, it is possible to process the film unit subsequent to distribution of the liquid processing composition in the presence of actinic radiation and thereby eliminate the need to provide a processing chamber within the camera and/or make it possible to withdraw the film unit from the camera almost immediately following distribution of the processing liquid. Binding element 20, strip 44 and the material comprising container 16 are also formed of a material opaque to actinic radiation to prevent exposure of the imagerecording medium by light entering the laminated assembly at the edges thereof. The opacifying agent is selected for its suitability as a background for viewing the dye-transfer image formed in the dyeable polymeric layer as well as for its opaque property. Another factor considered in the selection of the opacifying agent is the requirement that it does not interfere with the formation and color integrity of the dye-transfer image in the image-receiving sheet and that the agent be aesthetically pleasing and does not provide a noisy background that may degrade the image or detract from the information content thereof. Opacifying agents particularly desirable for incorporation in the liquid processing composition are those providing a white background for viewing the transfer image and particularly those compositions conventionally employed to provide a background for photographic reflection prints and having optical properties particularly suited for the reflection of incident radiation.

As examples of suitable opacifying agents mention may be made of barium sulfate, zinc oxide, titanium dioxide, barium stearate, silver flake, silicates, alumina, zirconium oxide, zirconium acetyl acetate, sodium zirconium sulfate, kaolin, mica and the like. An opacifying agent especially preferred because of its highly reflective properties is titanium dioxide and where it is desired to increase the opaqueness of the processing composition containing, for example, titanium dioxide, beyond that ordinarily obtained, an additional opacifying agent such as carbon black maybe added in a concentration of about one part carbon black to 500 parts titanium dioxide. A liquid processing composition suitable for incorporation in container 16 for use in combination with sheet materials of the type disclosed in the foregoing example is as follows:

Water Potassium Hydroxide Hydroxyethyl cellulose (high viscosity) [commercially available from Hercules Powder Co, Wilmington, Delaware, under the trade name Natrasol 250] N-benzyl-a-picolinium l bromide Benzotriazole Titanium dioxide grams grams grams coin gram grams illustrated in FIG. 5 of the drawings, by moving the film unit with container 16 foremost relative to and between a pair of juxtaposed members for applying compressive pressure first to the container to eject the fluid contents of the container between the photosensitive and imagerecording sheets 12 and 14 and then spread processing liquid 18 in a uniform, thin layer between sheets over an area at least coextensive with opening 22 in binding element 20. As previously noted, the processing liquid includes an agent for increasing the viscosity of the liquid so as to promote openingof the discharge passage of the container throughout substantially its entire length and facilitate the discharge of the liquid from the container and spreading of the liquid between the sheets. For this purpose, the liquid should be quite viscous and contain the film-forming material in quantities sufficient to impart a viscosity in excess of 1000 centipoises at a temperature of 20 C., and preferably of the order of I000 to 200,000 centipoises at said temperature.

Preferred means for spreading the processing liquid in a thin layer of uniform predetermined thickness comprise a pair of cylindrical rolls 46 mounted in juxtaposition for rotation about axes located in a common plane and biased toward one another and/or mounted a fixed maximum distance apart so as to apply compressive pressure to the container and elements of the film unit during movement thereof between the rolls. During movement of the film unit between rolls 46, compressive pressure is initially applied to container 16 generating hydraulic pressure in liquid 18 effecting the rupture of the bond between longitudinal marginal sections 38 of the container and the discharge of liquid 18 in the form of an elongated mass between sheets 12 and 14 at end marginal portions 40 and 42 thereof. Continued movement of the film unit relative to and between spread rolls 46 causes advancement of the mass of liquid between the sheets toward the opposite end thereof and spreading of the liquid as a thin layer 48 of predetermined thickness between and in contact with the facing surfaces of the sheets. A number of expedients are possible for controlling the thickness of the layer of processing liquid distributed between sheets including means in the processing apparatus for appropriately gapping or spacing apart spread rolls 46 and/or components of the film unit capable of performing this function. The film unit illustrated in the drawings is adapted to be employed with cylindrical rolls with the thickness of the liquid layer 48 being controlled, as illustrated in FIGS. 5, 6 and 7, by components of the film unit itself. The spacing between spread rolls 46 and hence the thickness of the layer of processing liquid is determined by the thickness of the film unit at the lateral margins thereof. This thickness is in turn a function of the thickness of the photosensitive and second sheets 12 and I4 and the thickness of lateral edge portions 24 of binding element 20. Since the photosensitive and second sheets are of substantially uniform thickness throughout, the thickness of layer 48 of processing liquid is determined by the thickness of binding element 20 and is approximately twice the thickness of the binding element. In a typical film unit, for example, the binding element may have a thickness of the order of .002 inch and provide for spreading of the processing liquid in a layer having an initial depth of the order of .004 inch.

To insure spreading of the processing liquid to the edges of the area defined by opening 22 in the binding element and formation of a transfer image extending to the edges of this area, image-receiving sheet 14 is embossed at its margins to displace marginal portions 32, 36 and 42 out of the plane of the medial portion of sheet 14 toward sheet 12 by a distance or depth approximating the thickness of binding element 20 or, one-half of the desired initial thickness of the layer of secured to marginal portions 32 and end portion 36 of sheet 14 are wider than the sections of lateral edge portions 24 and end portion 28 secured to marginal portions 30 and end portion 34 of sheet 12. Strip 44 is also narrower than end portion 26 and as a result of this construction, during spreading of the processing liquid between sheets 12 and 14, the inner surfaces of the sheets will be spaced apart in lateral and end regions extending outside of the edges of opening 22 allowing processing liquid to enter these regions and provide a reservoir of liquid for effecting image-formation within the region of the exposed image-recording medium immediately adjacent the lateral and end edges of opening 22. Still another factor contributing to the assurance of a complete spread is the presence of an excess quantity of the processing liquid. The processing liquid is initially spread as shown in FIGS. 5, 6 and 7 in a layer having a depth approximately twice the thickness of the binding element and calculated to provide aqueous liquid sufficient to permeate the layer containing the photosensitive medium and effect formation of a diffusion transfer image. As the liquid permeates the photosensitive layer and is absorbed and/or dissipated by sheets 12 and 14, the thickness of layer 48 is reduced and the film-forming agent becomes increasingly solid to provide a dimensionally stable opaque layer providing a background for the transfer image and tending to adhere the sheets to one another to form a laminate in which the integrity of the film unit structure is pre served. The depth of embossing of image-receiving sheet 14 approximates the final thickness of layer 48 to provide an integral, laminated structure of substantially uniform thickness throughout in which layer 48 and the image extend to the edges of opening 22 in binding element 20.

As previously noted, the film unit of the invention is designed to be processed by movement between spread rolls 46 to distribute the processing liquid in a layer that is continuous, is of uniform depth and extends throughout the entire area within opening 22 of binding element 20. During spreading, liquid 18 is advanced between the sheets as a mass located immediately ahead of spread rolls 46 and extending from side-to-side of the region defined by opening 22. The binding elements at the lateral margins of the sheets function to prevent escape of the processing liquid and also air so that air, located between the sheets during spreading of the processing liquid, must be advanced ahead of the mass of liquid and must be permitted to escape at the trailing end of the film unit or it will tend to inhibit the advancement of the mass of liquid.

As previously noted, in order to insure distribution of the liquid in a layer of uniform, minimum, predetermined depth over the entire exposed region to the trailing end thereof and allow some tolerance in the manufacture and filling of the container as well as the depth of the layer of liquid, it is considered necessary to provide excess processing liquid. This makes it necessary to provide for collecting and retaining the excess processing liquid within the film unit at the trailing end thereof and prevent the caustic liquid from escaping and contaminating the apparatus, e.g., camera, in which the film unit is processed or coming into contact with the operator. Collection and retention of the processing liquid is accomplished by providing a space or spaces within the film unit in which the processing liquid is trapped or collected and from which the processing liquid cannot be squeezed by the pressure-applying members employed to spread the liquid. The liquid collecting and retaining means must not only retain excess processing liquid within the film unit, but at the same time are required to release air from the film unit so that it does not interfere with spreading of the processing liquid.

In the preferred form of the film unit shown in the drawings, excess processing liquid is required to be collected and retained within trapping spaces provided within the bounds of the trailing end region of the film unit, that is, between the edge of the image area and the trailing edge of the film unit. It will be apparent that not only is the space available severely limited but that an excess liquid reservoir will be located in close proximity to the image-containing region between the sheets thereby presenting additional problems. First, the liquid collecting and retaining (also termed trapping") system must be designed to prevent escape of the liquid and accordingly binding element 20 which forms a part of the liquid collecting and retaining system is preferably formed of a substantially liquid impermeable material such as a polymeric film, waterproof paper or the like, which is also substantially impermeable to gas. This means that air, advanced between the sheets ahead of the processing liquid, may also tend to be trapped together with excess processing liquid interfering with the complete spread of the liquid and accordingly, provision must be made for releasing the air without permitting excess liquid to escape.

A second problem is the backflow of excess processing liquid from the reservoir or trapping space into the image area due to either or both the tendency for trapped air to be compressed by the pressure-applying members and then expand after movement of the film unit from between the pressure-applying members and any tendency of the sheet materials to stretch under pressure and generate hydraulic pressure within the trapped liquid. A third problem which has already been noted is the presence of the reservoir of excess processing liquid immediately adjacent and/or in direct communication with the space between the sheets containing the image and the resultant tendency for the liquid to migrate from the reservoir into the image-containing area where it may adversely effect the image.

According to the present invention a partial answer to the foregoing problems lies in collecting and retaining excess processing liquid externally of the sheets between which the image is formed within the film unit between one of the sheets and a trailing end portion of binding element 20. An embodiment of the trapping means of the invention is shown in FIGS. 2, 3, 6 and 7 of the drawings as including an elongated, generally comb-shaped spacing element 50 adapted to be secured between the trailing end portion of one of the sheets, preferably photosensitive sheet 12, and trailing end section 28 of binding element 20 to provide trapping spaces therebetween in which excess processing liquid is collected and retained. Spacing element 50 is substantially equal in length to the width of the sheets,

is relatively narrow having a width approximating or slightly less than the width of the trailing end border and includes a longitudinal section 52, uniformly spaced teeth 54 extending from the longitudinal section, and end sections 56 in the form of widened teeth extending from the ends of longitudinal section 52.

Longitudinal section 52 is formed with recess 58 located intermediate teeth 54. Spacing element 50 is formed of a relatively incompressible material, organic plastics adapted to molding processes being preferred, and has a thickness of the order of one to three times the thickness of the photosensitive and second sheets, the thickness of the spacing element depending upon the quantity of excess processing liquid to be collected and retained.

Spacing element 50 is secured between trailing end portion 28 of binding element 20 and end marginal portion 34 of photosensitive sheet 12 with teeth 54 extending toward the trailing end of the film unit to at least the trailing edge of the photosensitive sheet to provide between the teeth, photosensitive sheets and binding element, spaces or reservoirs opening toward the trailing end of the film unit. End marginal section 28 of binding element 20 is adhered along its edge (trailing) to photosensitive sheet 12 adjacent longitudinal section 52 of the spacingelement and may also be adhered to the outer surfaceof the spacing element with the inner surface thereof being adhered to the photosensitive sheet thereby further insuring integrity of the structure. At least the medial portion of the photosensitive sheet, i.e., the portion located intermediate end sections 56 of the spacing element, is shorter than the second sheet 14 so that the trailingedge of the photosensitive sheet is spaced inwardly as shown in the drawings from the trailing edge of the second sheet. In the form shown in FIG. 2, the photosensitive sheet includes extended sections 60 at its lateral edges corresponding to end sec tions 56 and extending beyond the trailing edge of the medial portion of the photosensitive sheet to substantially the trailing edge of the second sheet.

During processing of the film unit, as shown in FIGS. 5, 6 and 7, the processing liquid is advanced as a mass between sheets 12 and 14 by and ahead of pressureapplying rolls 46 toward the trailing end of the film unit and any excess processing liquid is spread beyond the trailing edge of the image area between the trailing end marginal portions 34 and 36 of sheets 12 and 14 and thence beyond the trailing edge of photosensitive sheet 12. As the pressure rolls pass over the trailing end section of the film unit, they press together the inner facing surfaces of the trailing end marginal portions 34 and 36 securely laminating these portions to one another by virtue of the fact that these portions have been wetted by the liquid so as to activate the adhesive properties of the adjacent hydrophilic strata and there is no layer of liquid between the strata to weaken the bond formed by pressing the sheets and strata together. Moreover, the additional-thickness of the film unit in this region provides for the application of increased compressive pressure further insuring the formation of a secure bond between the sheets in the region of the trailing edges. The teeth 54 of spacing element 50, being incompressible, function to hold apart the facing surfaces of sheet 12 and trailing end portion 28 of binding element 20 in the same region thereby providing a space exterior of the two sheets into which the excess processing liquid is free to flow. End section 56 of spacing element 50 and extended section 60 of sheet 12 extend to the trailing edge of sheet 14 and cooperate to maintain the space within the binding element between the trailing edge of sheet 12 and the trailing edge of sheet 14 required to enable the excess processing liquid to flow from between the sheets into the trapping spaces between the teeth of the spacing element.

Recesses 58 are provided in longitudinal section 52 of the spacing element to permit air to escape from the trapping spaces between the teeth and two alternative constructions may be incorporated in the film unit for releasing air from between the binding element and sheet 12. In the form shown in FIG. 2, end portion 28 of the binding element is formed with a plurality of very small perforations or pin holes 62 each located in alignment with a recess 58 and being large enough to pass air freely but too small to pass the viscous processing liquid. It should be apparent that this is also a characteristic of recesses 58 which are also quite small and, accordingly will inhibit, if not absolutely preclude, the passage of the viscous liquid while allowing the free passage of air. In an alternative embodiment, the seal or bond between trailing end portion 28 and sheet 12 is interrupted in spaced regions, that is, spaced regions are left unbonded or unsealed, to provide passages for he e cape 9 a r .whlehbas P$$SJBKQP1J rses In a slightly modified embodiment of the film unit, photosensitive sheet 12 is formed with a continuous straight trailing edge extending from side to side (i.e., without extended sections 60) and spacing element 50 is provided with end sections 56 as shown in FIG. 4 formed with thickened portions 66. The increased thickness of thickened portions 66 of end sections 56 is approximately equal to the thickness of photosensitive sheet 12, the thickened portions being located between the trailing edge of the photosensitivesheet and the trailing edge of the second sheet for spacing apart the pressure-applying rolls and maintaining the space within the binding element between the trailing edges of the sheets through which excess processing liquid v flows from between the sheets into the trappingspaces.

The embodiment of the film unit show n in FIG. 9 includes another embodiment of a spacing element designated 70 shown in detail in FIG. 8. Spacing element 70 comprises a narrow strip of a relatively thick sheet material, e.g. three to four times the thickness of the sheets, such as a polymer, paper, pressboard or the like, formed with large, regularly arranged, circular openings 72 having a diameter exceeding half the width of the spacing element and occupying the major portion of the volume of the spacing element. The spacing element, in the form shown, preferably includes a row of openings 72 centrally located and two rows of partial openings 72 in the form of indentations in the margins of element 70. In the form of film unit shown in FIG. 9, the second or image-receiving sheet 14 is longer than photo-sensitive sheet 12 and includes an end section 36 extending beyond the trailing edge of sheet 12 by approximately half the width of spacing element 70. The components of the film unit are essentially the same as previously described except that sheet 14 is not embossed at its margins toward sheet 12. The trailing end section 28 of binding element 20 is secured tothe outer surface of sheet 12 confining spacing element 70 be- 65 tween section 28, the outer surface of sheet l2 and a surface of section 36 of sheet 14 which is located externally of the region between sheets 12 and 14 in which a visible image is formed. The trailing edge of sheet 12 may be approximately aligned with the centers of the central row of openings 72 and/or at least overlaps a row of openings 72 permitting excess processing liquid to flow into spaces provided behind sheet 12 by the openings in the spacing element.

It should be noted and appreciated that the novel liquid collecting and retaining system of the invention provides substantially the largest possible trapping space within the confined space available within the bounds of the trailing end margins of the film unit and that this space and the reservoir contained therein are located externally of the two sheets of the film unit and at a maximum distance from the image-containing space between the sheets. Moreover, the transport system provides for a maximum security sea] at the trailing end of the image-containing space insuring that excess processing liquid and/or air cannot migrate back into the image-containing space to impair the image contained between the sheets. Trapping of excess processing liquid is effected within the region of the trailing end border of the laminated product in such a way as to be unobtrusive and not to impair the overall appearance or utility of the photographic print which the product comprises.

Since certain changes may be made in the above produce without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a photographic film unit adapted to be processed by a viscous, liquid processing composition distributed within said film unit from the leading end of said film unit toward the trailing end thereof by movement of said film unit between pressure-applying membe'rs, said film unit comprising a photosensitive sheet having a trailing edge section and a second sheet having a trailing edge section and secured in face-to-face relation with said photosensitive sheet, the improvement comprising:

retaining means securing said sheets in face-to-face relation with said trailing edge section of one of said sheets extending beyond at least a portion of said trailing edge section of the other of said sheets; said retaining means including a retaining sheet engaged around and secured to the outer surfaces of said trailing edge sections of said photosensitive and second sheets; and a spacing element secured between said retaining sheet and the outer surface of said trailing edge section of said other sheet, providing a space therebetween for collecting excess processing liquid distributed toward the trailing end of said film unit be yond the trailing edge of said other sheet, whereby said excess processing liquid is collected and retained external to the portions of said photosensitive and second sheets in face-to-face relation, said space provided by said spacing element permitting said excess processing liquid to flow, at least in part, beyond the trailing edge section of said other sheet and then in a direction of flow exterior of said other sheet toward the leading end of said film unit. 2. A photographic film unit as defined in claim 1 wherein said retaining sheet is perforated in the region of said space provided by said spacing element between said retaining sheet and said other sheet to permit air to escape from said space.

3. A photographic film unit as defined in claim 1 of said film unit and includes spaced sections extending at least to the trailing edge of said portions of said other sheet.

5. A photographic film unit as defined in claim 4 wherein said spaced sections extend beyond the trailing end of said other sheet substantially to the trailing edge of said one sheet.

6. A photographic film unit as defined in claim 4 wherein said spacing element includes end sections extending adjacent the lateral edges of said film unit beyond the trailing edge of said other sheet to the trailing edge of said one sheet, said end sections including portions thicker than the remaining portions of said end sections by substantially the thickness of said other sheet and located intermediate the trailing edges of said sheet.

7. A photographic film unit as defined in claim 1 wherein said spacing element is generally comb-shaped including a longitudinal section extending from side to side of said film unit and spaced teeth extending from said longitudinal section toward and to at least the trailing edge of said portion of said other sheet.

8. A photographic film unit as defined in claim 7 wherein said teeth extend beyond said trailing edge of said other sheet substantially to the trailing edge of said one sheet.

9. A photographic film unit as defined in claim 7 wherein said other sheet includes lateral trailing edge sections extending to the trailing edge of said one sheet and a medial section having a trailing edge spaced inwardly from said trailing edge of said one sheet.

10. A photographic film unit as defined in claim 9 wherein said spacing element includes end sections secured between said lateral trailing edge sections of said other sheet and said retaining sheet.

11. A photographic film unit as defined in claim 7 wherein said longitudinal section and said teeth of said comb-shaped spacing element cooperate with said retaining sheet and said other sheet to define spaces between said retaining sheet, said other sheet, and said teeth for collecting processing liquid, and said longitudinal section includes recesses intermediate said teeth for permitting air to escape from said spaces.

12. A photographic film unit as defined in claim 11 wherein said retaining sheet is adhered to said outer surface of said other sheet adjacent said longitudinal section of said spacing element throughout substantially the entire length of said spacing element except for spaced regions permitting air to escape from between said retaining sheet and said other sheet.

13. A photographic film unit as defined in claim 11 wherein said retaining sheet is perforated in the region of said recesses in said longitudinal section to permit air to escape from said spaces.

14. A photographic film unit as defined in claim 1 wherein said spacing element comprises a narrow strip of substantially rectangular sheet material formed with a plurality of regularly arranged circular openings for collecting and retaining said excess processing fluid.

15. A photographic film unit as defined in claim 14 wherein said circular openings are arranged in a row centrally positioned between the longitudinal margins of said spacing element and said spacing element further includes two rows of partial openings in the form of indentations in the longitudinal margins of said spacing elements. 

2. A photographic film unit as defined in claim 1 wherein said retaining sheet is perforated in the region of said space provided by said spacing element between said retaining sheet and said other sheet to permit air to escape from said space.
 3. A photographic film unit as defined in claim 1 wherein said retaining sheet is adhered to said spacing element and to said other sheet adjacent the edge of said spacing element furthest from the trailing end of said film unit.
 4. A photographic film unit as defined in claim 1 wherein said spacing element extends from side to side of said film unit and includes spaced sections extending at least to the trailing edge of said portions of said other sheet.
 5. A photographic film unit as defined in claim 4 wherein said spaced sections extend beyond the trailing end of said other sheet substantially to the trailing edge of said one sheet.
 6. A photographic film unit as defined in claim 4 wherein said spacing element includes end sections extending adjacent the lAteral edges of said film unit beyond the trailing edge of said other sheet to the trailing edge of said one sheet, said end sections including portions thicker than the remaining portions of said end sections by substantially the thickness of said other sheet and located intermediate the trailing edges of said sheet.
 7. A photographic film unit as defined in claim 1 wherein said spacing element is generally comb-shaped including a longitudinal section extending from side to side of said film unit and spaced teeth extending from said longitudinal section toward and to at least the trailing edge of said portion of said other sheet.
 8. A photographic film unit as defined in claim 7 wherein said teeth extend beyond said trailing edge of said other sheet substantially to the trailing edge of said one sheet.
 9. A photographic film unit as defined in claim 7 wherein said other sheet includes lateral trailing edge sections extending to the trailing edge of said one sheet and a medial section having a trailing edge spaced inwardly from said trailing edge of said one sheet.
 10. A photographic film unit as defined in claim 9 wherein said spacing element includes end sections secured between said lateral trailing edge sections of said other sheet and said retaining sheet.
 11. A photographic film unit as defined in claim 7 wherein said longitudinal section and said teeth of said comb-shaped spacing element cooperate with said retaining sheet and said other sheet to define spaces between said retaining sheet, said other sheet, and said teeth for collecting processing liquid, and said longitudinal section includes recesses intermediate said teeth for permitting air to escape from said spaces.
 12. A photographic film unit as defined in claim 11 wherein said retaining sheet is adhered to said outer surface of said other sheet adjacent said longitudinal section of said spacing element throughout substantially the entire length of said spacing element except for spaced regions permitting air to escape from between said retaining sheet and said other sheet.
 13. A photographic film unit as defined in claim 11 wherein said retaining sheet is perforated in the region of said recesses in said longitudinal section to permit air to escape from said spaces.
 14. A photographic film unit as defined in claim 1 wherein said spacing element comprises a narrow strip of substantially rectangular sheet material formed with a plurality of regularly arranged circular openings for collecting and retaining said excess processing fluid.
 15. A photographic film unit as defined in claim 14 wherein said circular openings are arranged in a row centrally positioned between the longitudinal margins of said spacing element and said spacing element further includes two rows of partial openings in the form of indentations in the longitudinal margins of said spacing elements. 